Magnetic core and coil assembly having improved insulation arrangement



' y 1957? c. T. WILLIAMS MAGNETIC CORE AND COIL ASSEMBLY HAVING IMPROVED INSULATION ARRANGEMENT s 1 m w t, r h Mm s 2 4 3 b 2 r.

m w m United States Patent 3,317,875 MAGNETIC CORE AND COIL ASSEMBLY HAVING IMPROVED INSULATION ARRANGEMENT Charles T. Williams, Fort Wayne, Ind., assignor to General Electric Company, a corporation of New York Filed Nov. 15, 1965, Ser. No. 507,763 6 Claims. (Cl. 336198) The invention relates to a magnetic core and coil assembly having an improved insulation arrangement, and particularly to such an insulation arrangement for a generally rectangular coil that is prewound, then provided with the insulation arrangement, and then placed on the magnetic core.

Many inductive devices, such as power transformers or ballasts for gaseous discharge lamps, are mass-produced by being assembled from prewound coils of insulated wire and punched laminations of magnetic material. The laminations are stacked and placed in and around the prewound coils to form the desired magnetic core structure. The assembled coils and laminations are held together by any suitable means, such as clamps. After the device is completed, its coil windings are usually given a high voltage breakdown testwith respect to the magnetic core to determine if there is suificient insulation between the coil windings and the magnetic core.

Generally, it has been found that almost all of the inductive devices which failed this high voltage breakdown test did so because of the insulation breakdown between the corners of the prewound coils positioned in the open ings in the magnetic core. Because the inductive devices tend to fail the high voltage breakdown test at the corners, added pieces of insulation have been provided at these corners. However, where the inductive devices are massproduced, each added piece of insulation and its corresponding assembly step appreciably increase the cost of the inductive devices.

Accordingly, an object of the invention is to provide a magnetic core and coil assembly having an improved insulation arrangement.

Another object of the invention is to provide an improved insulation arrangement that can be precut and placed on an electrical coil with a magnetic core to provide insulation at points of high voltage stress.

Another object of the invention is to provide a single precut piece of insulation that can be easily folded and placed on a prewound, rectangular electrical coil.

Another object of the invention is to provide a single precut piece of electrical insulation that can be easily placed and fitted on a prewound electrical coil to insulate the coil at points of possible voltage breakdown to an associated magnetic core.

Briefly, these and other'objects are achieved in accordance with the invention by a core and coil assembly having a single sheet of insulation that is precut to fit on the coil, which is prewound. The sheet of insulation has an inner cover that fits against the inner surfaces of the prewound coil, and four tabs that are integral with the inner cover and that are folded to fit against the coil winding thickness and a portion of the outer surfaces of the prewound coil. The fitted sheet of insulation is simply and easily fastened to the coil to insulate the corners of the coil most subject to high voltage breakdowns with the core. An added insulation may also be used.

The invention is particularly pointed out in the claims. The invention may be better understood from the following description given in connection with the accompanying drawing, in which:

FIGURE 1 shows a transformer, with parts broken .away to provide sectional views, to show Where the insulation arrangement of the invention can be advantageously used;

FIGURE 2 shows a development of the insulation arrangement in accordance with the invention for a prewound coil which can be used in the transformer of FIG- URE 1;

FIGURE 3 shows an exploded prespective view of a prewound electrical coil, the precut and folded electrical insulation arrangement of FIGURE 2 in accordance with the invention, and an insulation wrapper;

FIGURE 4 shows the insulation arrangement of FIG- URES 2 and 3 in accordance with the invention during assembly with the prewound coil of FIGURE 3; and

FIGURE 5 shows the prewound coil with the assembled insulation arrangement of FIGURES 2, 3, and 4 in accordance with the invention.

FIGURE 1 shows a ballast transformer which is typical of an inductive device that uses prewound rectangular coils, and that can use the insulation arrangement of the invention advantageously. The transformer shown in FIGURE 1 is assumed to include first and second windings 10, 12 coupled on a shell-type magnetic core comprised of stacked E-shaped laminations 14 and I-shaped laminations 16. Such a core is shown in greater detail in Patent No. 2,882,506 granted to Brooks et al. on Apr. 14, 1959. The E-shaped laminations 14 and the I-shaped lamination-s 16 are punched to provide four windows or openings through which the two windings 10, 12 respectively pass. The windings 10, 12, as shown in the broken away portion of FIGURE 1, comprise a plurality of turns 19 which surround the I-shaped laminations 16 along its longitudinal axis. Generally, the windings 10, 12 are prewound of insulated (usually enamel) wire, but they generally require additional insulation. The transformer is assembled with thel-shaped laminations 16 within the windings 10, 12, and the E-shaped laminations 14 around the windings 10, 12. The assembled transformer may be held in the desired fixed relation with suitable clamp-s 18 placed on at the ends of the laminations 14, 16. As mentioned above, in an inductive device such as the transformer shown in FIGURE 1, the most common points of high voltage breakdown are at the eight corners 20 of the windings It), 12 near the magnetic core. Two reasons for high voltage breakdowns occurring at these corners are that the coil or wire insulation is subject to wear at these corners 20, and that the relative sharpness (and hence voltage stress) ofthe coils and rangement in accordance with the invention. This insulation arrangement can be advantageously used with a rectangular coil, such as the coils that form the windings, 10, 12 of FIGURE 1. The insulation arrangement of FIGURE 2 may be formed from any suitable sheet insulating material, such as 0.019 inch thick lamination having asbestos paper between two polyester films. In

FIGURE 2, cuts or outside edges are shown by solid lines, and folds are shown by dashed lines. The insulation arrangement shown in FIGURE 2 comprises an elongated, substantially rectangularly shaped inner cover 26. The cover 26 has a length, from left to right as viewed in FIGURE 2, that preferably exceeds twice the coil inner length plus twice the coil inner height. The inner cover 26 has a width equal substantially to the coil width. Integral with the inner cover 26 are four substantially rectangular tabs or ears 28 which are symmetrically positioned on the inner cover 26. Two tabs 28 are positioned on one side of the inner cover 26, and two tabs 28 are positioned on the other side of the inner cover 26 at corresponding positions. Each of the tabs 28 has an undercut 30 at each end. The undercuts 30 of each tab 28 extend toward each other along the longitudinal sides of the inner cover 26 to points separated by a distance substantially equal to the inner length of the coil. The adjacent undercuts 30 of the tabs 28 on one side of the cover have end points that are separated by a distance substantially equal to the inner height of the coil. The tabs 28 have a transverse dimension that is approximately twice the coil winding thickness so that the tabs 28 can be folded to provide a coil thickness cover 32 and an outer surface cover 34 for the coil, as will be explained.

FIGURE 3 shows a perspective view of an electrical coil which could form one of the windings 10, 12 of FIGURE 1, and shows the insulation arrangement of FIGURE 2 when folded and ready for assembly into the coil. The coil of FIGURE 3 has external leads 40 connected to it, with the connections covered by a short insulation strip 42. FIGURE 3 also shows an insulation wrapper 44 which may be placed around the insulation arrangement after it has been placed on the coil, or placed on the coil before the insulation arrangement. The coil has a length (inner or outer), height (inner or outer), and width which are mutually perpendicular, and also has a winding thickness, all of these being indicated in FIGURE 3. The insulation arrangement shown in FIGURE 3 is formed by folding the tabs 28 of the development of FIGURE 2 downward along each longitudinal dashed line, and by folding the inner cover 26 of the development upward along each transverse dashed line. The inner cover 26 forms a four sided rectangle which fits inside the coil. The tabs 28 are substantially parallel to the coil length, with the thickness covers 32 substantially parallel to the coil thickness surfaces, and with the outer covers 34 substantially parallel to the plane formed by the coil length and width. The insulation material at the folds in the tabs 28 covers each of the eight corners of the coils (along the length) that are in the vicinity of the magnetic core. In the case of the coil of FIGURE 3, the coil turns along the length are intended to pass through the openings in the magnetic core. A proper fit of the insulation arrangement with the coil is obtained by making the inner cover fold spacings slightly smaller than the inner coil length and height, and by making the thickness cover transverse fold at a point slightly beyond the coil winding thickness. The inner cover overlap may be any suitable amount, and the outer cover transverse dimension may also be any suitable amount, but preferably at least enough to go around the corner and provide good insulation for the coil.

FIGURE 4 shows the stage. of assembling the insulation arrangement within the coil. It will be seen that the projections of the tabs 28 must be depressed or bent so that the insulation arrangement can be placed in the inner opening of the coil. This canbe easily done if the insulation has sufficient resiliency, and the tabs 28 will return to their normal position. If desired, the insulation arrangement only can be used, in which case a piece of tape can be wrapped transversely around each pair of tabs on the coil legs to hold the insulation arrangement in position. If the wrapper 44 is to be used, it can be placed on the coil before the insulation arrangement, or can be placed over the insulation arrangement after it is in place. In either case, the insulation arrangement is easily put on, and easily and simply held in place. FIG- URE 5 shows the coil with the wrapper 44, and with the insulation arrangement over the wrapper 44. In FIGURE 5, the tabs 28 are shown in their normal protective position, with a piece of tape 46 holding the insulation arrangement on each coil leg. With reference to FIGURE 1, it will be seen how the assembled coil, insulation arrangement, and wrapper (shown in FIGURE 5) fit on the core, and provide insulation at the corners (along the coil length) and on the inner and outer surfaces of the coil in the vicinity of the core.

It will thus be seen that the invention provides an improvide insulating arrangement for a substantially rectangular electrical coil for any inductive device, particularly shell-type magnetic cores. The insulating arrangement is easily manufactured, and is easily assembled on a prewound coil. The insulation arrangement can be held in position on the coil by one piece of tape or similar material on each of two coil legs. The insulation arrangement provides insulation at the points of greatest voltage stress. Persons skilled in the art will appreciate that modifications of the invention may be made. For example, the overlap'of the ends of the inner cover 26 may be increased or decreased. Likewise, the transverse dimension of the outer cover 34 of the tabs 28 may be increased or decreased, as long as the outer covers 34 extend around the corners ofthe coil. Therefore, while the invention has been described with reference to particular embodiments, it is to be understood that modifications may be made without departing from the spirit of the invention or from the scope of the claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A magnetic core and coil'assembly comprising at least one substantially rectangular prewound electrical coil having a length, a height, a' width, and a winding thickness, and having winding turns that are substantially parallel to a plane passing through said length and height of said coil, a shell-type magnetic core having at least two winding openings therein, said coil being mounted on said core with a portion of said winding turns along said coil length being positioned in said winding openings, and a sheet of relatively thin insulation material consisting of an essentially rectangular inner cover and further consisting of four symmetrically positioned tabs integral therewith, each of said tabs being essentially rectangular and extending transversely from opposite longitudinal edges of said inner cover, two of said tabs extending along one longitudinal edge of said inner cover and the other two of said tabs extending along the other longitudinal edge of said cover, each of said tabs being longitudinally undercut along its respective longitudinal edge of said inner cover from opposite ends of said tabs to points separated by a distance substantially equal to the inner length of said coil, said insulation material being formed with transverse folds in said inner cover so that said inner cover .fits against the inner surfaces of said coil, and being further formed with a first longitudinal fold in each of said tabs between said separated points and by a second longitudinal fold in each of said tabs that is transversely and outwardly spaced from said first longitudinal fold by a distance slightly greater than said coil winding thickness so that each of said tabs covers two respective corners of said coil along said coil length in said opening.

2. The'assembly of claim l'wherein an insulation Wrapper is placed over said fitted insulation along the outer surfaces of said coil. i

3. The assembly of claim 1 wherein an insulation wrapper is placed around the outer length and height surfaces of said coil between said coil and said fitted insulation.

4. A coil assembly for a magnetic core having a substantially rectangular prewound electrical coil having a predetermined inner length and inner height, having a predetermined winding thickness and width, and having a predetermined outer length and height, said arrangement comprising: a sheet of relatively thin insulation material consisting of a substantially rectangular inner cover having a longitudinal length substantially equal to twice said inner length plus said inner height and a transverse width substantially equal to said winding width, and further consisting of four symmetricaly positioned tabs integral therewith, each of said tabs being substantially rectangular and extending transversely from opposite longitudinal edges of said inner cover, two of said tabs extending along one longitudinal length of said inner cover and the other two of said tabs extending along the other longitudinal length of said inner cover at corresponding positions, each of said tabs having a longitudinal length greater than said inner length and being inwardly and longitudinally undercut along said inner cover length from opposite ends to points separated by a distance substantially equal to said inner length, said insulation arrangement being formed by four transverse folds in said inner cover that are respectively and longitudinally spaced from one end of said inner cover by substantially half said inner height, by substantialy said inner length, by substantialy said inner height, and by substantially said inner length so that said inner cover fits against the inner surfaces of said coil, and being further formed by a first longitudinal fold in each of said tabs that is between said separated points and by a second longitudinal fold in each of said tabs that is transversely and outwardly spaced from said first longitudinal fold by a distance slightly greater than said coil winding thickness so that each of said tabs fits against a respective surface of said coil along said length thickness and against a respective portion of the outer surface of said coil along the outer length. 5. The arrangement of claim 4 wherein the ends of said fitted inner cover overlap by a predetermined amount along one of said inner surfaces of said coil.

6. The arrangement of claim 4 wherein an insulation wrapper is placed over said fitted insulation arrangement around the outer length and height surfaces of said coil.

References Cited by the Examiner UNITED STATES PATENTS 2,055,899 9/1936 Hurt 33620'8 X 2,858,514 10/1958 Henderson 336-198 X LEWIS H. MYERS, Primary Examiner. E. GOLDBERG, Assistan! Examiner. 

1. A MAGNETIC CORE AND COIL ASSEMBLY COMPRISING AT LEAST ONE SUBSTANTIALLY RECTANGULAR PREWOUND ELECTRICAL COIL HAVING A LENGTH, A HEIGHT, A WIDTH, AND A WINDING THICKNESS, AND HAVING WINDING TURNS THAT ARE SUBSTANTIALLY PARALLEL TO A PLANE PASSING THROUGH SAID LENGTH AND HEIGHT OF SAID COIL, A SHELL-TYPE MAGNETIC CORE HAVING AT LEAST TWO WINDING OPENINGS THEREIN, SAID COIL BEING MOUNTED ON SAID CORE WITH A PORTION OF SAID WINDING TURNS ALONG SAID COIL LENGTH BEING POSITIONED IN SAID WINDING OPENINGS, AND A SHEET OF RELATIVELY THIN INSULATION MATERIAL CONSISTING OF AN ESSENTIALLY RECTANGULAR INNER COVER AND FURTHER CONSISTING OF FOUR SYMMETRICALLY POSITIONED TABS INTEGRAL THEREWITH, EACH OF SAID TABS BEING ESSENTIALLY RECTANGULAR AND EXTENDING TRANSVERSELY FROM OPPOSITE LONGITUDINAL EDGES OF SAID INNER COVER, TWO OF SAID TABS EXTENDING ALONG ONE LONGITUDINAL EDGE OF SAID INNER COVER AND THE OTHER TWO OF SAID TABS EXTENDING ALONG THE OTHER LONGITUDINAL EDGE OF SAID COVER, EACH OF SAID TABS BEING LONGITUDINALLY UNDERCUT ALONG ITS RESPECTIVE LONGITUDINAL EDGE OF SAID INNER COVER FROM OPPOSITE ENDS OF SAID TABS TO POINTS SEPARATED BY A DISTANCE SUBSTANTIALLY EQUAL TO THE INNER LENGTH OF SAID COIL, SAID INSULATION MATERIAL BEING FORMED WITH TRANSVERSE FOLDS IN SAID INNER COVER SO THAT SAID INNER COVER FITS AGAINST THE INNER SURFACES OF SAID COIL, AND BEING FURTHER FORMED WITH A FIRST LONGITUDINAL FOLD IN EACH OF SAID TABS BETWEEN SAID SEPARATED POINTS AND BY A SECOND LONGITUDINAL FOLD IN EACH OF SAID TABS THAT IS TRANSVERSELY AND OUTWARDLY SPACED FROM SAID FIRST LONGITUDINAL FOLD BY A DISTANCE SLIGHTLY GREATER THAN SAID COIL WINDING THICKNESS SO THAT EACH OF SAID TABS COVERS TWO RESPECTIVE CORNERS OF SAID COIL ALONG SAID COIL LENGTH IN SAID OPENING. 